US4490699A - Intermediate frequency band-pass filter - Google Patents

Intermediate frequency band-pass filter Download PDF

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Publication number
US4490699A
US4490699A US06/498,455 US49845583A US4490699A US 4490699 A US4490699 A US 4490699A US 49845583 A US49845583 A US 49845583A US 4490699 A US4490699 A US 4490699A
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United States
Prior art keywords
intermediate frequency
frequency band
pass filter
shield plate
trap
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
US06/498,455
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English (en)
Inventor
Hiroyuki Yanagida
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Alps Alpine Co Ltd
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Alps Electric Co Ltd
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Assigned to ALPS ELETRIC CO., LTD., 1-7 YUKIGAYA OTSUKA-CHO, OTA-KU, TOKYO, JAPAN, A CORP. OF JAPAN reassignment ALPS ELETRIC CO., LTD., 1-7 YUKIGAYA OTSUKA-CHO, OTA-KU, TOKYO, JAPAN, A CORP. OF JAPAN ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: YANAGIDA, HIROYUKI
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/205—Comb or interdigital filters; Cascaded coaxial cavities
    • H01P1/2053—Comb or interdigital filters; Cascaded coaxial cavities the coaxial cavity resonators being disposed parall to each other

Definitions

  • the present invention relates to an intermediate frequency band-pass filter suitable for use in a converter in a community antenna or wire television receiver.
  • CATV system Community antenna or wire television broadcasting systems
  • CATV system television programs are transmitted from a broadcasting station through cables, and television receivers in subscriber's homes select a desired channel out of the received channels. Since the CATV system can have a wide frequency band irrespective of other broadcasting systems, the CATV system is assigned a large number of channels.
  • the television receiver has a frequency converter of the superheterodyne type for selecting a desired channel out of a number of channels and converting the frequency of the selected channel into a predetermined intermediate frequency.
  • the above object can be achieved by providing a shield plate disposed between resonators constituting a double tuning circuit and having a coupling window, the shield plate having in an edge thereof a step which serves as a trap.
  • FIG. 1 is a block diagram of a converter in a conventional wire television receiver
  • FIG. 2 is a circuit diagram of an intermediate frequency band-pass filter in the converter of FIG. 1;
  • FIG. 3 is an enlarged perspective view of an intermediate frequency band-pass filter according to the present invention.
  • FIG. 4 is a front elevational view of a shield plate in the filter shown in FIG. 3;
  • FIG. 5 is a circuit diagram of an equivalent circuit of the filter of FIG. 3.
  • FIG. 6 is a graph showing the measured high-frequency characteristics of the intermediate frequency band-pass filter of FIG. 3 and a prior intermediate frequency band-pass filter.
  • FIG. 1 shows in block form a conventional frequency converter, which comprises an input terminal 1, an input filter 2, a mixer 3, a local oscillator 4, an intermediate frequency filter 5, an intermediate frequency amplifier 6, a mixer 7, a local oscillator 8, an output filter 9, and an output terminal 10.
  • a number of channels transmitted over a cable are supplied through the input terminal 1 and the input filter 2 to the mixer 3, in which the frequencies are mixed with a signal having a frequency f L1 (hereinafter referred to as a "first oscillation frequency signal") supplied from the local oscillator 4.
  • a signal having a frequency f L1 hereinafter referred to as a "first oscillation frequency signal" supplied from the local oscillator 4.
  • the oscillation frequency f L1 from the local oscillator 4 is variable so that a desired channel to be selected out of the channels transmitted through the input terminal 1 will be in a predetermined frequency band.
  • the mixer 3 produces as its output each channel with its frequency converted to allow the desired channel to have the predetermined frequency band.
  • the output from the mixer 3 is supplied to the intermediate frequency band-pass filter 5.
  • the intermediate frequency band-pass filter 5 is designed to pass therethough the foregoing predetermined frequency band. Therefore, it only passes the desired channel selected out of the supplied channels.
  • the signal in the desired channel is amplified by the intermediate frequency amplifier 6, and the amplified signal is fed to the mixer 7, in which it is mixed with a signal having a frequency f L2 (hereinafter referred to as a "second oscillation frequency signal") delivered from the local oscillator 8.
  • the oscillation frequency f L2 generated by the local oscillator 8 is fixed.
  • the frequency of the desired channel is converted by the mixer 7 into a certain frequency which is fed through the output filter 9 to the output terminal 10.
  • the input filter 2 and the intermediate frequency band-pass filter 5 have pass bands designed such that they are sufficiently different from the range which the oscillation frequency f L1 from the local oscillator 4 can take, and are capable of sufficiently suppressing the first oscillation frequency signal which leaks from the mixer 3.
  • the oscillation frequency f L2 of the local oscillator 8 be selected in the vicinity of the pass band of the intermediate frequency band-pass filter 5.
  • the second oscillation frequency signal which has leaked from the mixer 7 is supplied through the intermediate frequency amplifier 6 to the intermediate frequency band-pass filter 5, and the blocking characteristics of the the intermediate frequency band-pass filter 5 cannot be sharper than a certain degree, the second oscillation frequency signal is not sufficiently suppressed by the intermediate frequency band-pass filter 5 and is fed to the mixer 3.
  • the second oscillation frequency signal is then mixed with the first oscillation frequency signal, producing a beat signal having a frequency f L1 -f L2 . Since the frequency of the beat signal falls sometimes within the pass band of the input filter 2, the beat signal tends to pass through the input filter 2 and the input terminal 1 into the cable, not shown.
  • a CATV system having a full-channel frequency range of 55 MHz to 445 MHz is characterized by:
  • Oscillation frequency f L1 of the local oscillator 4 605 MHz-995 MHz
  • Resonant frequency of the intermediate frequency band-pass filter 5 550 MHz
  • Oscillation frequency f L2 of the local oscillator 8 605 MHz
  • the leaking second oscillation frequency signal is accordingly liable to be supplied to the mixer 3 without being sufficiently suppressed by the intermediate frequency band-pass filter 5.
  • Such a beat signal When such a beat signal is generated and discharged, it will be transmitted through the cable and received by other television receivers. If the other television receivers select a channel containing the beat signal, the selected channel is disturbed by the beat signal.
  • FIG. 2 is a circuit diagram showing such a prior intermediate frequency band-pass filter, which is composed of an input terminal 11, a capacitor 12, tuning capacitors 13, 14, tuning coils 15, 16, a trap coil 19, a trap capacitor 20, and an output terminal 21.
  • the tuning circuit of the tuning capacitor 13 and the tuning coil 15, and the tuning circuit of the tuning capacitor 14 and the tuning coil 16 jointly form a double tuning circuit for providing a prescribed pass band.
  • a desired channel which falls in the prescribed pass band is selected out of a number of channels which are represented by an output signal from the mixer 3 (FIG. 1) through the input terminal 11, and is supplied through the output terminal 21 to the intermediate frequency amplifier 6 (FIG. 1).
  • the intermediate frequency band-pass filter includes a trap circuit composed of the trap coil 19 and the trap capacitor 20.
  • the trap frequency is selected to be the oscillation frequency f L2 of the local oscillator 8 for preventing the second oscillation frequency signal from going from the output terminal 21 to the input terminal 11.
  • the resonators which form the tuning circuits are surrounded by a frame and placed respectively in two regions separated by a shield plate, the shield plate having a coupling window through which the tuning coils 15, 16 (FIG. 2) of the resonators are coupled.
  • the intermediate frequency band-pass filter has had the following shortcomings:
  • the intermediate frequency band-pass filter is costly to fabricate as additional electronic parts are required to assemble the trap circuit and a process is needed to attach the trap circuit. Since constants of the electronic parts vary, the trap frequency has to be adjusted.
  • An expensive temperature-compensation capacitor is necessary for the temperature compensation of the trap circuit. Since the trap circuit is inserted in the intermediate frequency band-pass filter where the impedance is low, the trap circuit cannot have a high Q, failing to supress the second oscillation frequency signal to a sufficient degree.
  • FIG. 3 shows an intermediate frequency band-pass filter according to the present invention.
  • the filter comprises a frame composed of frame members 22 1 , 22 2 , 22 3 , 22 4 , 22 5 , a shield plate 23 having a coupling window 24 and an upper edge 25 cut out to provide a step or rectangular recess 26.
  • the frame members 22 1 , 22 2 , 22 3 , 22 4 serve as side walls, the frame member 22 5 as a bottom, and a frame member (not shown) is used as a cover. These frame members jointly form a hollow region.
  • the shield plate 23 extends between the side walls 22 1 , 22 2 to devide the hollow region into two spaces in which the resonators are mounted respectively.
  • the coupling window 24 in the shield plate 23 serves to couple helical coils 15, 16 which are tuning coils, the degree of coupling being determined by the shape of the coupling window.
  • the step 26 formed in the upper edge 25 of the shield plate 23 serves as a window when the cover is placed over and closes the hollow region.
  • the window provides communication between the two spaces separated by the shield plate 23.
  • the step 26 in the shield plate 23 can provide a trap in the intermediate frequency band-pass filter.
  • the trap frequency is determined by the width of the step 23 in the direction normal to the side wall 22 1 or 22 2 .
  • the width of the step 23 is selected such that the trap frequency is equal to the oscillation frequency f L2 of the local oscillator 8 (FIG. 1).
  • FIG. 4 is a front elevational view of the shield plate of FIG. 3. Like or corresponding parts in FIG. 4 are indicated by like or corresponding reference numerals in FIG. 3 and will not be described.
  • FIG. 5 shows an equivalent circuit of the intermediate frequency band-pass filter illustrated in FIG. 3. Like or corresponding parts in FIG. 5 are denoted by like or corresponding reference numerals in FIG. 2. With this arrangement, the double tuning circuit has a trap or frequency signal suppression capability, and there is no need for an additional trap circuit.
  • FIG. 6 shows measured high-frequency characteristics of intermediate frequency band-pass filters.
  • the graph has a vertical axis indicative of the amount of suppression, and a horizontal axis indicative of the frequency.
  • the solid-line curve represents the characteristics of the intermediate frequency band-pass filter of the present invention, while the dotted-line curve represents the characteristics of the prior intermediate frequency band-pass filter.
  • the characteristic curves in FIG. 6 were plotted when the oscillation frequency f L2 of the local oscillator 8 (FIG. 1) was 620 MHz. Study of FIG. 6 clearly shows that the frequency was suppressed by the filter of the invention sufficiently to the extent that is about 15 dB higher than by the conventional filter.
  • the present invention is also applicable to other uses than intermediate frequency band-pass filters in CATV converters.
  • the numerical data referred to in the above description are by way of example only, and should not be interpreted as being limitative.
  • a desired trap can be formed by cutting out a step in an edge of a shield plate having a coupling window through which resonators are coupled with each other.
  • the trap frequency is determined solely by the configuration of the step, no trap frequency adjustment is required. Accordingly, the intermediate frequency band-pass filter of the invention is less costly to fabricate, and can provide a desired frequency suppression capability.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Filters And Equalizers (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)
US06/498,455 1982-05-27 1983-05-26 Intermediate frequency band-pass filter Expired - Fee Related US4490699A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP1982076893U JPS58182501U (ja) 1982-05-27 1982-05-27 中間周波帯域炉波器
JP57-76893[U] 1982-05-27

Publications (1)

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US4490699A true US4490699A (en) 1984-12-25

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US06/498,455 Expired - Fee Related US4490699A (en) 1982-05-27 1983-05-26 Intermediate frequency band-pass filter

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JP (1) JPS58182501U (ja)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1986001956A1 (en) * 1984-09-24 1986-03-27 Ma John Yoh Han Catv converter having improved tuning circuits
US4661998A (en) * 1983-09-22 1987-04-28 Matsushita Electric Industrial Co. Ltd. Double superheterodyne tuner
US5032807A (en) * 1989-07-10 1991-07-16 General Instrument Corporation Notch filter using helical transmission line and coaxial capacitor
US5036302A (en) * 1989-06-19 1991-07-30 U.S. Philips Corporation Radio receiver filter with image rejection
AU626688B2 (en) * 1989-06-19 1992-08-06 Philips Electronics Australia Limited A filter
US5157363A (en) * 1990-02-07 1992-10-20 Lk Products Helical resonator filter with adjustable couplings
US5508668A (en) * 1993-04-08 1996-04-16 Lk-Products Oy Helix resonator filter with a coupling aperture extending from a side wall
WO2005091426A1 (en) * 2004-03-22 2005-09-29 Filtronic Comtek Oy Arrangement for dividing a filter output signal
US20080048801A1 (en) * 2006-08-23 2008-02-28 Frontier Electronics Co., Ltd. Coupling filter device with specific coupling coefficient
CN104934669A (zh) * 2015-06-15 2015-09-23 华南理工大学 一种带宽可控的双频螺旋腔滤波器

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2819391A (en) * 1954-03-25 1958-01-07 Sol L Reiches Superheterodyne tuner with image frequency trays which tracks with local oscillator and antenna resonators
US3337791A (en) * 1964-08-20 1967-08-22 Rca Corp Frequency multiplier
US3621484A (en) * 1970-03-05 1971-11-16 Motorola Inc Helical resonator having variable capacitor which includes windings of reduced diameter as one plate thereof

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2819391A (en) * 1954-03-25 1958-01-07 Sol L Reiches Superheterodyne tuner with image frequency trays which tracks with local oscillator and antenna resonators
US3337791A (en) * 1964-08-20 1967-08-22 Rca Corp Frequency multiplier
US3621484A (en) * 1970-03-05 1971-11-16 Motorola Inc Helical resonator having variable capacitor which includes windings of reduced diameter as one plate thereof

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4661998A (en) * 1983-09-22 1987-04-28 Matsushita Electric Industrial Co. Ltd. Double superheterodyne tuner
WO1986001956A1 (en) * 1984-09-24 1986-03-27 Ma John Yoh Han Catv converter having improved tuning circuits
US4619000A (en) * 1984-09-24 1986-10-21 John Ma CATV converter having improved tuning circuits
US5036302A (en) * 1989-06-19 1991-07-30 U.S. Philips Corporation Radio receiver filter with image rejection
AU626688B2 (en) * 1989-06-19 1992-08-06 Philips Electronics Australia Limited A filter
US5032807A (en) * 1989-07-10 1991-07-16 General Instrument Corporation Notch filter using helical transmission line and coaxial capacitor
US5157363A (en) * 1990-02-07 1992-10-20 Lk Products Helical resonator filter with adjustable couplings
US5508668A (en) * 1993-04-08 1996-04-16 Lk-Products Oy Helix resonator filter with a coupling aperture extending from a side wall
WO2005091426A1 (en) * 2004-03-22 2005-09-29 Filtronic Comtek Oy Arrangement for dividing a filter output signal
US20060252400A1 (en) * 2004-03-22 2006-11-09 Filtronic Comtek Oy Arrangement for dividing a filter output signal
US7466970B2 (en) 2004-03-22 2008-12-16 Filtronic Comtek Oy Arrangement for dividing a filter output signal
CN1774832B (zh) * 2004-03-22 2010-06-23 菲尔特朗尼克科姆特克有限公司 用于分配滤波器输出信号的设备
US20080048801A1 (en) * 2006-08-23 2008-02-28 Frontier Electronics Co., Ltd. Coupling filter device with specific coupling coefficient
US7609131B2 (en) * 2006-08-23 2009-10-27 Prosperity Dielectrics Co., Ltd. Coupling filter device with specific coupling coefficient
CN104934669A (zh) * 2015-06-15 2015-09-23 华南理工大学 一种带宽可控的双频螺旋腔滤波器
CN104934669B (zh) * 2015-06-15 2018-02-27 华南理工大学 一种带宽可控的双频螺旋腔滤波器

Also Published As

Publication number Publication date
JPS58182501U (ja) 1983-12-05
JPS631441Y2 (ja) 1988-01-14

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Owner name: ALPS ELETRIC CO., LTD., 1-7 YUKIGAYA OTSUKA-CHO, O

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:YANAGIDA, HIROYUKI;REEL/FRAME:004136/0817

Effective date: 19830224

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Effective date: 19921227

STCH Information on status: patent discontinuation

Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362